Synergism of epidermal growth factor receptor-targeted immunotherapy with photodynamic treatment of ovarian cancer in vivo

Background. Epithelial ovarian cancer often develops resistance to standard treatments, which is a major reason for the high mortality associated with the disease. We examined the efficacy of a treatment regimen that combines immunotherapy to block the activity of epidermal growth factor receptor (EGFR), overexpression of which is associated with the development of resistant ovarian cancer, and photodynamic therapy (PDT), a mechanistically distinct photochemistrybased modality that is effective against chemo- and radioresistant ovarian tumors. Methods: We tested a combination regimen consisting of C225, a monoclonal antibody that inhibits the receptor tyrosine kinase activity of EGFR, and benzoporphyrin derivative monoacid A (BPD)-based PDT in a mouse model of human ovarian cancer. Therapeutic efficacy was evaluated in acute treatment response and survival studies that used 9-19 mice per group. Analysis of variance and Wilcoxon statistics were used to analyze the data. All statistical tests were two-sided. Results: Mice treated with PDT + C225 had the lowest mean tumor burden compared with that in the no-treatment control mice (mean percent tumor burden = 9.8%, 95% confidence interval [CI] = 2.3% to 17.3%, P <.001). Mean percent tumor burden for mice treated with C225 only or PDT only was 66.6% (95% CI = 58.7% to 74.4%, P <.001) and 38.2% (95% CI = 29.3% to 47.0%, P <.001), respectively. When compared with PDT only or C225 only, PDT + C225 produced synergistic reductions in mean tumor burden (P<.001, analysis of variance) and improvements in survival (P =.0269, Wilcoxon test). Median survival was approximately threefold greater for mice in the PDT + C225 group than for mice in the no-treatment control group (80 days versus 28 days), and more mice in the PDT + C225 group were alive at 180 days (3/9; 33% [95% CI = 7% to 70%]) than mice in the C225-only (0/12; 0% [95% CI = 0% to 22%]) or PDT-only (1/10; 10% [95% CI = 0.2% to 44%]) groups. Conclusion: A mechanistically non-overlapping combination modality consisting of receptor tyrosine kinase inhibition with C225 and BPD-PDT is well tolerated, effective, and synergistic in mice.